Astronomers have found a planetary body lurking at the edge of our Solar System, and they've named it DeeDee. DeeDee, which stands for Distant Dwarf, was first discovered late 2016, but little was known about its physical structure. Now, new data from the Atacama Large Millimeter/submillimeter Array (ALMA) has revealed details about the mysterious object's true identity – and it's even bigger than scientists expected.
According to new data, DeeDee is about two-thirds the size of the dwarf planet Ceres, the largest member of our asteroid belt, and has enough mass to be spherical.
This means DeeDee fulfils the criteria necessary to be termed a dwarf planet, although astronomers have yet to give it that official label. DeeDee sits on the edge of our Solar System, approximately 92 astronomical units from the Sun, which is roughly 137 billion kilometres (86 billion miles) in space lingo.
It's so far out there that it takes 13 hours for the light from DeeDee to reach Earth, making it the second most distant known trans-Neptunian object (TNO) with an orbit second only to the dwarf planet Eris.
In fact, DeeDee's orbit is so large that it takes 1,100 years to complete just one lap of the Sun. And its discovery suggests we still have a lot to learn about the objects that lurk at the very depths of our Solar System.
"Far beyond Pluto is a region surprisingly rich with planetary bodies, some are quite small but others have sizes to rival Pluto, and could possibly be much larger." said lead researcher David Gerdes from the University of Michigan.
Just because these objects are far way, doesn't mean they're not important. Planetary objects such as DeeDee are remnants from the creation of our planetary system. It's hoped that getting more insight into how and when they were made might help us solve one of the longest standing mysteries in planetary science – how the planets in our Solar System, including Earth, originally formed.
But actually finding these distant planetary bodies is another matter, which is why the discovery of DeeDee is so exciting. DeeDee was first spotted using a Blanco telescope at the Cerro TololoInter-American Observatory in Chile.
The discovery was part of a Dark Energy Survey that churned out nearly 15,000 images and identified more than 1.1 billion objects, most of which have turned out to be stars and distant galaxies. Only a tiny fraction of these objects turn out to anything of interest within our own Solar System.
Nevertheless, last year, astronomers identified what appeared to be a TNO lurking on 12 of the 15,000 images, and they informally named it DeeDee. But without follow-up observations from ALMA – a set of radio antennas that can recreate clearer images of distant space – they couldn't tell if DeeDee was small but highly reflective, or large but extremely dark.
"ALMA picked it up fairly easily, we calculated that this object would be incredibly cold, only about 30 degrees Kelvin, just a little above absolute zero." said Gerdes.
Using DeeDee's heat signature, the astronomers were able to confirm that DeeDee was uncommonly large, but so dark that it only reflected about 13 percent of the sunlight that reached it. In other words, DeeDee was about as bright as a candle placed halfway to the Moon.
The discovery of DeeDee confirms that modern technology is finally capable of detecting extremely distant and slow moving objects on the edges of our Solar System. Perhaps now these same technologies could even be used to find the hypothesized Planet Nine that is predicted to orbit far beyond DeeDee and Eris.
Wherever the discovery leads us, finding DeeDee has given us all a glimpse into the mysterious unknown.
The research has been published in the Astrophysical Journal Letters.